Preparation of thin, highly directionalized filament structures



July 27, 1965 o. w. SELBY PREPARATION OF THIN HIGHLY DIRECTIONALIZED FILAMENT STRUCTURES Filed Sept. 29. 1961 INVENTOR DONALD W. SE LBY ATTORNEY United States Patent PREEARATHQN 3F THEN, HIGHLY DIREC- TZQIJALEZED FEAR ZEN? STRiJQTURES Donald W. Selby, Wihnington, DeL, assignor to E. l. du

Pont de Nemours and Company, Wilmington, DeL, a

r oration of Delaware w p Filed ept. 29, 1961, Ser. No. 141,819

3 Claims. (Cl. 156181) This invention relates to an improved process for male ing bonded non-woven spread yarn structures having superior properties to those available heretofore.

It is well known to prepare non-woven structures involving the spreading of large denier multifilament yarns into broad thin ribbons and combining these ribbons to form non-woven sheet structures. However, it has been found difficult, if not impossible, heretofore, to prepare wide, thin lightweight non-woven sheet structures containing hi hly directionalized filaments spread uniformly throughout their width with substantially all of the mdividual filaments being essentially parallel to each other.

One of the objects or this invention is to provide a simplified and continuous process for the preparation of such thin, non-woven sheet structures referred to above. Another object is to provide continuous lengths of wide, lightweight, bonded non-woven sheet structures in which the individual filaments are uniformly spaced. A further object is to provide useful articles of commerce such as bagging fabrics from such non-woven sheet structures, said fabrics having superior properties for use in packaging heavy materials such as fertilizers which are susceptible to damage from moisture. Other objects will appear below.

The above objects are accomplished by providing a novel continuous process for preparing lightweight bonded non-woven filamentary structures. The process comprises the steps of stripping a plurality of multifilarnent yarns having substantially zero twist from a creel, feeding said yarns in the form of a Warp to a reed, guiding said warp of yarns through a spreading zone while maintaining the yarns sufficiently taut to prevent filament entanglement, electrostatically spreading the individual filaments in the yarns in a spreadin zone by contacting each yarn and filament with the surface of a series of glass rods, applying a binder composition to the uniformly spread warp offilaments issuing from the spreading zone while maintaining the individual filaments in their spaced relationship in the warp sheet, hardening the binder to fix the position of the filaments and then winding up the bonded non-woven sheet material. The invention also comprehends certain useful products resulting from the above process which are in the form of-bonded non-woven sheet material of uniform thickness composed of a plurality of continuous filaments substantially all of which are essentially parallel to each i 7 material being at least 12 inches wide and weighing less 7 than about 2 oz./yd.

A suitable method for practicing this invention is illustrated schematically in FEGURE 1. Multifilament yarn is stripped from creel 2 and fed as a warp to a reed 3. The Warp of yarns is fed to feeding rolls 4 and then in contact with glass rods 5 whereby the individual filaments in the yarns are spread. The spread Warp of filaments is picked up by pulling rolls 6 and upon ex ting from the rolls is coated with binder 7 issuing from applicator 8, which may comprise a spray gun or an extruder. The binder impregnated warp sheet of filaments is carried on conveying apron ll and goes through a drying zone 9 which may comprise an oven and is wound on a warp beam 19.

The multifilament yarns for use in the process of this invention must have substantially zero twist in order to be handled properly and lead to uniform sheet material having a combination of superior properties. Thus, the yarn must contain between zero and about one-half turn per inch of twist, and preferably less than about onequarter turn per inch, either S or Z. The individual filaments in the yarn bundle should be preferably less than about eight denier per filament.

Normally the process will operate more smoothly and will produce greater uniformity in the product if the yarns contain less than the normal amount of spin finish.

Preferably, the yarns should contain less than about 0.3%

by weight of standard spin finish, the composition of which will vary depending upon the composition of the filaments, and examples of which are well known in the textile art.

The composition of the filaments in the yarn is not critical. They must be multifilament yarns from any of the well lmown continuous filaments, either synthetic or natural; for example, polyamides, such as polyhexamethylene adiparnide and polycaproamide; polyesters, such as ethylene terephthalate polymers and copolymers, acrylic polymers and copolymers such as polyacrylonitrile, vinyl polymers such as polyvinyl chloride and polyvinylidene chloride, fiuorinated ethylene polymers such as polytetrafiuoroethylene and polytrifiuoromonochloroethylene, polyhydrocarbons such as linear polyethylene, linear polypropylene and copolymers of ethylene with other polymerizable monomers, regenerated cellulose, cellulose acetate, polyurethanes and the like. Also suitable for use in this invention are filament yarns from natural sources, such as silk, glass, and the like. However, the preferred multifilament yarns for use in this process are those made from hydrophobic synthetic organic polymeric filaments, since this class of filaments in general leads to superior properties in the bonded non-woven products of this invention. The filaments making up the yarns must be continuous filaments, but they may be crimped or uncrimped.

The conditions under which the individual filaments in the yarn bundles are spread or separated in the spread ing zone are critical to achieving uniformity in the final products of this invention. It is important that the atmosphere surrounding the yarns and filaments be under controlled humidity from the creel up to the point of bonding the spread filaments. From the point Where the warp of yarns enters the spreading zone to the point where the spread filament warp leaves the spreading zone, the filamentary material must be maintained just taut enough to prevent filament entanglement. This slight tension is normally achieved by two pairs of standard rolls, geared for a difierential speed so that the pulling set of rolls runs 3% to 5% faster than the feeding set.

In order for the individual filaments to separate from the yarn bundles and provide a warp of uniformly separated filaments issuing from the exit end of the spreading zone, an electrostatic charge is applied to the yarns. The electrostatic charge may be applied to the yarns by contacting them with supporting elements made of a variety of materials, provided the compositions of the yarn filaments and the composition of the supporting elements have sufiiciently different electrostatic potentials to provide such a static charge. One suitable method is to contact the surface of each synthetic organic polymeric yarn and filament with a series of glass rods. If the glass rods are stationary the relative humidity should be kept T) c3 below about but if the glass rods are rotated as the filamentary material contacts them, the relative humidity of the specified controlled humidity area may be 60% to 70%. One preferred arrangement using a series of stationary rods is illustrated in FIGURE 1, wherein one yarn is fed in contact with the upper surface of each rod, the next yarn is fed in contact with the lower surface of each rod, and so forth. By the provision of the series of glass rods and maintenance of controlled constant humidity in the spreading zone, enough static charge is imposed on the surface of the filaments by contact with the glass rods, to provide the necessary spreading force to separate the individual filaments from the yarn bundles. en the rods are stationary the differential speed will be constant, but when spaced rods rotate as a unit, the differential speed will pulsate.

After the warp of separated filaments issues from the exit end of the spreading zone, a binder composition is immediately applied uniformly over the surface area of the thin warp of spread filaments in order to stabilize the filaments in their spaced relationship from each other both widthwise and thickness-wise. Any suitable polymeric binder composition may be used; for example, thermoplastic and thermosetting resins, natural and synthetic elastomers such as polyethylene resin, acrylic resins, polyamide resins, polyester and alkyd resins, natural fiber, and the like. The binder composition should have a suitable viscosity at the point of application to the warp sheet of filaments, so that either it fills continuously the interstitial spaces between the horizontally spaced filaments including such spaces between the filaments vertically when the warp sheet is either two or three filaments thick, or it bonds together portions of the filaments at points or small areas. The binder composition may be applied as a solution of polymer in solvent, as a dispersion of polymer in a non-solvent, as an emulsion, or it may be applied as a hot-melt composition. The minimum amount of binder required is that amount sufficient to hold each spread filament separated from its neighbors, so that the sheet material may be handled on processing machinery without disturbing the essentially parallel and separated positioning of the filaments. After the application of binder to the warp sheet of filaments, the bonded and/or coated sheet is passed through a drying zone to evaporate any solvent or diluent present, or is cooled to solidify the binder if it is applied as a melt. Then the bonded filamentary sheet is wound up on conventional take-up rolls or on a warp beam. The binder may be applied by spraying, printing, doctoring, dipping, and the like.

The resulting thin, wide, lightweight, bonded, nonwoven filamentary sheet material which results from the above description has many uses as such; for example, as tapes and ribbons, tire chafer fabrics, protective coverings, and the like. This sheeting is superior to similar products made heretofore in that it possesses greater uniformity of filament spacing and a higher amount of unidirectionality of the filaments and has a much higher ratio of strength to thickness.

This thin strong sheeting also has many other uses by combining two or more layers of sheeting and/or combining the sheet with additional binder resins and laminating. For example, two, three or more of the sheets may be laminated together with the filament direction superimposed, or with alternate layers of the sheets arranged so that the filament direction crosses at a fixed angle, for example, to each other or 90 to each other. Also a composite of three or more sheets may be laminated together with the filaments arranged in three definite directions with respect to each other. Two or more of the thin sheets may be combined or laminated using more of the same binder composition or using a different binder composition by hot-pressing the sheets together at predetermined angles of orientation between the respective filamentary directions. Alternatively, one

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of the thin sheets may be laminated to films (e.g., polyethylene terephthalate film), woven, knitted or other non-woven fabrics, felts, and the like. instead of using purely laminating techniques, one or more layers of the thin, bonded sheet materials of this invention may be attached to fabrics using other known means of attachment (e.g., sewing), or combinations of other means of attachment, together with conventional hot-pressing and laminating techniques may be used with or without the use of additional binder or resin. When using the bonded thin sheeting of this invention to laminate several sheets together or to laminate a sheet to another layer of material, many useful articles of commerce may be produced taking advantages of the high moduluahigh bursting strength and high tear strength of the thin sheets of this invention. Examples of some of these additional useful articles of commerce include premium bagging fabrics, heavy-duty wrapping, tents and tarpaulins, chafer fabrics and ply fabrics for use in tires, reinforcement for plastic laminates, pressure sensitive tapes, polishing and wiping cloths, wall coverings, aprons, cable insulation, luggage linings, interlinings and interfacings for apparel, laundry bags, lamp shades, tool bags, pipe wrap and the like.

The novel thin sheeting of this invention may contain small amounts of additives, such as coloring materials, heat and light stabilizers, pigments, fillers, delustrants, and the like provided that the amount of additive is not suitcient to detract from the combination of the superior strength and other properties inherent in the thin sheeting. The sheeting may be dyed, printed, calender-ed, embossed or otherwise treated before or after combining with additional layers or laminating to other substrates.

T18 following example illustrates a preferred manner of practicing the present invention, although it is understood that the invention is not limited to the preferred materials and conditions outlined below.

Example I A series of spools containing polyhexamethylene adipamide continuous multifilament yarn (840 denierfilaments0.1 t.p.i. Z twist), containing 0.2% by weight of conventional nylon spin finish, were mounted on a creel. Each of these yarns was stripped from the top of the spools in order to remove most of the twist in the yarn, and was then fed by conventional warp beaming technology to a reed. From there, the yarns were fed as a warp containing an average of 7 /2 yarn ends per inch of width at a speed of 10 yards per minute through a pair of feeding rolls to the entrance end of a spreading zone. These yarns were placed under just enough tension to keep the spreading of the filaments straight by running the pulling rolls at about 3% faster surface speed than that of the feeding rolls. The spreading zone contained a series of four stationary glass rods (each rod one inch in diameter) arranged longitudinally one behind the other in the direction in which the yarns were fed to the spread-J ing zone. Each yarn was fed over the top surfaces of the whole set of glass rods or under the bottom surfaces of the set of rods, the yarns next to each other alternating with its neighbors over, under, over, under, etc. The atmosphere surrounding the yarns was maintained at 20% relative humidity. A thin warp sheet of spaced individual filaments (each 6 d.p.f.) issued from the nip of the pulling rolls at the exit end of the spreading zone. Immediately after exit from this nip, the warp sheet of filaments was coated with a layer of molten polyethylene resin fed from an extrusion head positioned above the Warp sheet. The molten resin issued from the extrusion head in the form of a sheet approximately the same width (20 inches) as the width of the warp sheet and the polyethylene sheet was applied to the warp sheet of filaments at an angle of approximately 30. After application of the polyethylene coating the coated warp sheet of filaments was led through a cooling zone to solidify the molten resin.

The solidified polyethylene resin formed a coating of approximately mils in thickness and penetrated through the thickness of the warp sheet of filaments, which varied between one and three filaments thick throughout substantially the entire length and width of the sheet, the average filament thickness being approximately 1.5 filaments. The cooled bonded sheet of filaments was then woundup on a beam. At this stage the bonded sheet was 0.0024 inch thick, 24 inches wide and weighed 1.8 oz./yd. The thin bonded sheet of separated filaments possessed a high strength-to-thickness ratio. The thickness of the sheet was very uniform, the spacing between each individual filament in the sheet was uniform and filaments were oriented to a high degree of parallelism in the same direction. This lightweight, non-woven bonded filamentary sheet is useful as such as a strong lightweight wrapping tape or ribbon.

Two of the above lightweight non-woven sheets were placed on top of each other with the filaments aligned at an angle of 90 to each other. These two sheets were then laminated by pressing between hot platens at about 150 C. to fuse the binder resin and consolidate the two sheets into one layer. The resulting laminate is useful as a bagging fabric and has high tear strength and high bursting strength.

Example 11 Polyhexarnethylene adiparnide continuous multifilament yarns (840 denier 140 filamentszero twist) were passed through a cold water bath to remove the spin finish and then dried. The yarns were then processed as described in Example 1 until a warp entered the spreading zone through feeding rolls. The spreading zone into which the warp was fed contained a rotating glass unit for generating the electrostatic charge on the yarns. T he glass unit consisted of three one inch glass rods held in fixed relation to the axis of the'unit and spaced apart equidistant about four inches from the axis. Alternate strands of yarn were fed over the top and under the bottom of the glass unit so each yarn was in rubbing contact with the surface of the glass rods. The glass unit was rotated through an independent drive at a speed of about 100 rpm. The atmosphere surrounding the yarns was about 70% relative humidity. The electrostatically spread filaments exited from the nip of the pulling rolls onto a poleythylene belt conveyor and immediately thereafter were treated with a binder to retain the spaced relationship between the filaments. The binder used in this example was formed from a viscous solution of cellulose acetate dissolved in acetone which was spun through a hypodermic needle having an opening of approximately 0.010 inch. The resulting spun acetate binder fiber was allowed to deposit laterally back and forth across the width of the running warp, so that each individual filament in the warp was held apart from its neighbors by the deposited binder fiber which was spaced about one inch apart in the warp direction. The cooled bonded 'sheet of filaments Was approximately 12 inches Wide and weighed 0.3 oz./yd. The bonded sheet of filaments varied between one and three filaments thick throughout substantially the entire length and width of the sheet, the average thickness being approximately 1.5 filaments. The thickness of the sheet was very uniform and the spacing between each individual filament was uniform. The filamerits in the sheet were oriented to a high degree of parallelism in the same direction. This non-woven bonded filamentary sheet was sandwiched between two layers of two mil polyethylene film and the whole heat pressed at about C. The resulting laminate is useful as a high strength tarpaulin fabric.

What is claimed is:

l. A continuous method of preparing thin, bonded, nonwoven sheet structures containing highly directionalized filaments spread uniformly throughout their width with substantially all of the individual filaments being essentially parallel to each other which comprises passing a warp of substantially zero-twist yarns through a spreading zone, pulling the yarns through said zone thus maintaining the yarns sufficiently taut to prevent filament entanglement, rubbing the filaments against a supporting element having a sufficiently different electrostatic potential to provide a static charge thereby electrostatically spreading the individual filaments of the yarn uniformly in said spreading Zone, maintaining the spaced relationship of the filaments of the warp exiting from the spreading Zone, applying a binder composition to the uniformly spread warp of filaments and setting the binder to retain the spaced relationship.

2. A continuous method of preparing thin, bonded, nonwoven sheet structures containing highly directionalized filaments spread uniformly throughout their width with substantially all of the individual filaments being essentially parallel to each other which comprises feeding a warp of substantially zero twist yarns from a reed into the nip of a set of feed rolls, maintaining the yarns taut by means of a set of pull rolls, rubbing the filaments against a supporting element having a sufiiciently different electrostatic potential to provide a static charge thereby electrostatically spreading the individual filaments of the yarns in the zone between the two sets of rolls to form a uniformly spaced wam of filaments, maintaining the spaced relationship between the filaments in the warp exiting from the pull rolls, applying a binder to the filament warp and setting the binder to retain the spaced relationship of filaments.

3. A method of preparing thin bonded nonwoven sheet structures containing highly directionalized filaments spread uniformly throughout their width with substantially all of the individual filaments being essentially parallel to each other comprising stripping a plurality of multifilament synthetic, organic, polymeric yarns having substantially zero-twist from a creel, feeding said yarns in the form of a warp to a reed, guiding said warp of yarns through a spreading zone pulling the yarns through said Zone thus maintaining the yarns sufficiently taut to prevent filament entanglement, electrostatically spreading the individual filaments of the yarns uniformly in said spreading zone by rubbing said filaments against a surface of a glass rod, applying a binder composition to the uniformly spread warp of filaments issuing from the spreading Zone while maintaining the spaced relationship, hardening the binder and then winding up the bonded, non-woven sheet material.

References tilted by the Examiner UNITED STATES PATENTS 2,354,702 8/44 PrOtZ 15453.6 2,625,498 1/53 Koch 156l80 2,738,298 3/56 David 154-536 2,825,199 3/58 Hicks 5736 2,953,893 9/60 Smith et al. 57-36 3,042,569 7/62 Paul l56166 3,046,632 7/62 Tsutsumi 28--1 EARL M. BERGERT, Primary Examiner. 

1. A CONTINUOUS METHOD OF PREPARING THIN, BONDED, NONWOVEN SHEET STRUCTURES CONTAINING HIGHLY DIRECTIONALIZED FILAMENTS SPREAD UNIFORMLY THROUGHOUT THEIR WIDTH WITH SUBSTANTIALLY ALL OF THE INDIVIDUAL FILAMENTS BEING ESSENTIALLY PARALLEL TO EACH OTHER WHICH COMPRISES PASSING A WARP OF SUBSTANTIALLY ZERO-TWIST YARNS THROUGH A SPREADING ZONE, PULLING THE YARNS THROUGH SAID ZONE THUS MAINTAINING THE YARNS SUFFICIENTLY TAUT TO PREVENT FILAMENT ENTANGLEMENT, RUBBING THE FILAMENTS AGAINST A SUPPORTING ELEMENT HAVING A SUFFICIENTLY DIFFERENT ELECTROSTATIC POTENTIAL TO PROVIDE A STATIC CHARGE THEREBY ELECTROSTATICALLY SPREADING THE INDIVIDUAL FILAMENTS OF THE YARN UNIFORMLY IN SAID SPREADING ZONE, MAINTAINING THE PSPACED RELATIONSHIP OF THE FILAMENTS OF THE WARP EXITING FROM THE SPREADING ZONE, APPLYING A BINDER COMPOSITION TO THE UNIFORMLY SPREAD WARP OF FILAMENTS AND SETTING THE BINDER TO RETAIN THE SPACED RELATIONSHIP. 